Isobutane reaction

Isobutane reactions, 13 698 Isobutane route, to methacrylic acid,... 

Here it should be noted that secondary C-H bond rupture is only slightly more probable than the scission of primary bonds, despite the fact that D(iso-C3H7—H) is 5-6 kcal./mole lower than D(m-C3Ht—H) (70,71). Hence, the bond-dissociation energy does not appear to be the major determining factor in the primary mode of decomposition. However, the results obtained by Palmer and Lossing (73) for the isobutane reaction do indicate that methyl substitution on the secondary position in propane causes C-H bond cleavage to occur preponderately at the tertiary site. 

The selectivity to octane and trimethylpentanes is satisfactory, but the lifetime of this catalyst is too short for industrial usage. However, with alternated isobutane/reaction mixture feeding the catalyst lifetime and productivity are increased several times (7 times for PFES and 35 times for PFPS). 

It is also interesting to note that the distance between the substrate and the zeolite framework in the TS was much larger for the isobutane reaction, where the attack was on a tertiary center, than for the linear alkanes, where the attack was on primary centers. A similar situation was found in the case of the exchange reactions [44]. Although the nature of the TS was the same for exchanging at primary, secondary and tertiary centers, in the last case the distance from the substrate (isobutane) to the zeolite framework is larger than for the other alkanes. This can be attributed to the steric hindrance of the methyl groups as the isobutane approaches the acid site. Thus, it is... 

Dimethvihexane Formation. Dimethyl hexane formation Is believed to result largely from reactions of butene-l. This includes (I) codimerization of butene-l and isobutene, (2) dimerization of butene-l, and (3) dimerization of isobutene, and (4) isomerization of dimethylhexyl carbonlum Ions each of these reactions is followed by abstraction of a hydride ion from isobutane. Reactions follow ... 

Additional discussions on the role of acid-soluble hydrocarbons as a reactant during alkylation has been discussed earlier (4,8,11). The acid-soluble hydrocarbons clearly act as a reservoir of hydride Ions. Hydride Ions are furnished to the acid-soluble hydrocarbons primarily from Isobutane (Reaction B of Table I) and they are withdrawn from the hydrocarbons principally by Reaction M-1. 

For the ethane and isobutane reactions the following values were obtained (in percentage of total) Rma 56%, fJabs 21%, and ffirecomb 23%, whilo for tetramethylsilane R b 36%, Rabs 12% and fBrecomb 52%. From this, the rate constant ratio for deactivation to insertion (fcd/ i) lor the (CHsl Si reaction is equal to ca. 1.8, the largest yet obtained. It is also seen that tetramethylsilane is a more efficient third body for the recombination of sulfur atoms than any of the hydrocarbons studied. 

Figure 1 Schematic of the oxidative dehydrogenation of isobutane reaction system.

In contrast to these experiments, phenol/isobutanal reactions (Table 3) gave mainly monoadducts. Only traces of hydroxyalkylphenols were observed apparently dehydration is a fast consecutive reaction under these conditions. 

Alkylation combines lower-molecular-weight saturated and unsaturated hydrocarbons (alkanes and alkenes) to produce high-octane gasoline and other hydrocarbon products. Conventional paraffin-olefin (alkane-alkene) alkylation is an acid-catalyzed reaction, such as combining isobutylene and isobutane to isooctane. 

These are effective high-octane gasoline additive oxygenates. The conversion of isobutane into isopropyl, methyl ketone, or isopentane into isobutyl, methyl ketone is illustrative. In this reaction, no branched carboxylic acids (Koch products) are formed. 

Because the protonation of ozone removes its dipolar nature, the electrophilic chemistry of HOs, a very efficient oxygenating electrophile, has no relevance to conventional ozone chemistry. The superacid-catalyzed reaction of isobutane with ozone giving acetone and methyl alcohol, the aliphatic equivalent of the industrially significant Hock-reaction of cumene, is illustrative. 

On the other hand, under superacidic conditions, alkanes are readily alkylated via front-side CJ-iasertion by carbocationic alkylating agents. The direct alkylation of the tertiary C—H CJ-bond of isobutylene with isobutane has been demonstrated (71). The stericaHy unfavorable reaction of tert-huty fluoroantimonate with isobutane gave a Cg fraction, 2% of which was 2,2,3,3-tetramethylbutane ... 

When usiag HF TaF ia a flow system for alkylation of excess ethane with ethylene (ia a 9 1 molar ratio), only / -butane was obtained isobutane was not detectable even by gas chromatography (72). Only direct O -alkylation can account for these results. If the ethyl cation alkylated ethylene, the reaction would proceed through butyl cations, inevitably lea ding also to the formation of isobutane (through /-butyl cation). 

Methyl /-Butyl Ether. MTBE is produced by reaction of isobutene and methanol on acid ion-exchange resins. The supply of isobutene, obtained from hydrocarbon cracking units or by dehydration of tert-huty alcohol, is limited relative to that of methanol. The cost to produce MTBE from by-product isobutene has been estimated to be between 0.13 to 0.16/L ( 0.50—0.60/gal) (90). Direct production of isobutene by dehydrogenation of isobutane or isomerization of mixed butenes are expensive processes that have seen less commercial use in the United States. 

Acetone is a coproduct of butane LPO. Some of this is produced from isobutane, an impurity present in all commercial butane (by reactions 2, 13, 14, and 16). However, it is likely that much of it is produced through the back-biting mechanisms responsible for methyl ketone formation in the LPO of higher hydrocarbons (216). 

Isobutane. Isobutane can be oxidized noncatalyticaHy to give predominantly /-butyl hydroperoxide [75-91-2] (TBHP) (reactions 2 and 3). The... 

The alkanes have low reactivities as compared to other hydrocarbons. Much alkane chemistry involves free-radical chain reactions that occur under vigorous conditions, eg, combustion and pyrolysis. Isobutane exhibits a different chemical behavior than / -butane, owing in part to the presence of a tertiary carbon atom and to the stability of the associated free radical. 

Reactions of /l-Butane. The most important industrial reactions of / -butane are vapor-phase oxidation to form maleic anhydride (qv), thermal cracking to produce ethylene (qv), Hquid-phase oxidation to produce acetic acid (qv) and oxygenated by-products, and isomerization to form isobutane. 

Isomerization. Stmctural isomerization of / -butane to isobutane is commercially useful when additional isobutane feedstock is needed for alkylation (qv). The catalysts permit low reaction temperatures which favor high proportions of isobutane in the product. The Butamer process also is well known for isomerization of / -butane. 

Typical heterogeneous Ziegler catalysts operate at temperatures of 70— 100°C and pressures of 0.1—2 MPa (15—300 psi). The polymerization reactions are carried out ia an iaert Hquid medium (eg, hexane, isobutane) or ia the gas phase. Molecular weights of LLDPE resias are coatroUed by usiag hydrogea as a chain-transfer ageat. 

All lation. The combination of olefins with paraffins to form higher isoparaffins is termed alkylation (qv). Alkylate is a desirable blendstock because it has a relatively high octane number and serves to dilute the total aromatics content. Reduction of the olefins ia gasoline blendstocks by alkylation also reduces tail pipe emissions. In refinery practice, butylenes are routinely alkylated by reaction with isobutane to produce isobutane—octane (26). In some plants, propylene and/or pentylenes (amylenes) are also alkylated (27). 

A simplified flow diagram of a modern H2SO4 alkylation unit is shown in Eigure 1. Excess isobutane is suppHed as recycle to the reactor section to suppress polymerization and other undesirable side reactions. The isobutane is suppHed both by fractionation and by the return of flashed reactor effluent from the refrigeration cycle. 

The hydrocarbon cracking operations that generate feed olefins generally do not produce sufficient isobutane to satisfy the reaction requirements. Additional isobutane must be recovered from cmde oil or natural gas Hquids or generated by other refinery operations. A growing quantity of isobutane is produced by the isomerization of / -butane [106-97-8]. 

Propylene. Propylene alkylation produces a product that is rich in dimethylpentane and has a research octane typically in the range of 89—92. The HF catalyst tends to produce somewhat higher octane than does the H2SO4 catalyst because of the hydrogen-transfer reaction, which consumes additional isobutane and results in the production of trimethylpentane and propane. 

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